1. Field of the Invention
The present invention relates to a clutch mechanism and a webbing winding device, for example, a webbing winding device having a pretensioner for rotating a spool in a webbing winding direction at a time when a vehicle suddenly decelerates, and a clutch mechanism used in this webbing winding device.
2. Description of the Related Art
A conventional webbing winding device 310 is shown in FIGS. 17 and 18.
In this webbing winding device 310 (see Japanese Patent Application Publication (JP-B) No. 2-10743), rolling bodies 320 are mounted in supporting pins 314 projecting from a cover 312. The rolling bodies 320 are inserted into notches 318 of a pulling member roller 316. Each rolling body 320 is normally spaced apart from an intermediate bush 324 and a belt shaft 322 is freely rotated independently of the pulling member roller 316.
When the pulling member roller 316 is rotated in the direction of arrow B when, for example, a vehicle suddenly decelerates, the supporting pins 314 are sheared by the rotating force of this pulling member roller 316, and the pulling member roller 316 and the intermediate bush 324 are connected to each other through the rolling bodies 320. Thus, the rotating force of the pulling member roller 316 is transmitted to the bel t shaft 322 and a pretensioner is operated so that slackening of the belt is removed.
Accordingly, shearing force for shearing the supporting pin 314 is required when the pretensioner is operated in this webbing winding device 310. However, this shearing force gives resistance to the rotation of the pulling member roller 316 and the torque for rotating the belt shaft 322 is reduced as a result.
In contrast to this, in a webbing winding device 350 (see Japanese Patent Application Laid-Open (JP-A) No. 8-133015) shown in FIG. 19, a sliding portion 354 is connected to base plate portion 352 by a thin, breakable connecting portion 356. Further, a roller pin holding portion 358 is disposed perpendicularly to the sliding portion 354. No roller pin 360 held by the roller pin holding portion 358 comes in contact with a sleeve 362 at a normal time. Accordingly, the possibility of the roller pins 360 influencing the pulling-out, winding, or the like of the webbing 364 is low.
When a large deceleration occurs in the vehicle and clutch outer teeth 366 are rotated in the direction of arrow C via a planetary gear device, the roller pins 360 bite into portions between an outer circumferential face of the sleeve 362 and cam faces 368 of the clutch outer teeth 366 due to the deformation of the roller pin holding portions 358. Thus, the clutch outer teeth 366 and the sleeve 362 are connected to each other and rotating torque of the clutch outer teeth 366 is transmitted to the sleeve 362 so that the pretensioner is operated. Further, when the clutch outer teeth 366 are rotated, the rotating drive force of the clutch outer teeth 366 are transmitted to a holder 370 through the roller pin 360 and the connecting portion 356 is broken. Accordingly, the clutch outer teeth 366 further rotate the sleeve 362 in the direction of the arrow C via the roller pin 360 so that a winding shaft 372 is rotated and the webbing 364 is tightened.
Accordingly, the connecting portion 356 is also broken when the pretensioner in this webbing winding device 350 is operated and this breaking gives resistance to the rotation of the clutch outer teeth 366 and torque for rotating the winding shaft 372 is reduced as a result.
Such a problem is not limited to the above webbing winding devices 310, 350, but is generally caused in a clutch mechanism for transmitting the rotating force of a rotating member to a member to be rotated by moving and nipping a transmitting member between the rotating member and the member to be rotated by breaking one portion of the transmitting member.